1. Field of the Invention
The present invention relates to powder for an electrolyte plate of a molten carbonate fuel cell, and a sheet and a molten carbonate fuel cell using it.
2. Description of Related Art
An existing molten carbonate fuel cell is constituted by stacking a plurality of unit cells through separators for forming flowing courses of reaction gases to the respective gas diffusing electrodes, and by connecting electrically the respective cells. Each of the unit cells comprises a pair of oppositely disposed gas diffusing electrodes, that is, a fuel electrode (anode) and an oxidant electrode (cathode), and an electrolyte plate which is interposed by these gas diffusing electrodes and carries an electrolyte of an alkali metal carbonate. The molten carbonate fuel cell is operated in such a manner that a carbonate is melted under high temperature, a fuel gas containing hydrogen and carbon monoxide is supplied to the fuel electrodes of the respective cells, and a gas mixture containing air and carbon dioxide is supplied to the oxidant electrodes.
An electrolyte plate is formed of an electrolyte consisting of an alkali metal carbonate, a carrying member for preventing the electrolyte, which becomes liquid under high temperature operation, from spilling, and a reinforcing member for preventing the crack from occurring during the rise and fall of temperature. And, as its manufacturing method, particles of the carrying member and reinforcing member, and an organic binder are dispersed in an organic solvent to prepare a slurry thereof, which is poured onto a carrier sheet, then, by use of a doctor blade, a green sheet is formed. Thereafter, the green sheet is degreased to form a sheet of a porous body having an appropriate pore structure (matrix sheet), then, to this sheet of a porous body, an alkali metal carbonate is impregnated. This is a prevailing manufacturing method.
Upon forwarding a larger capacity of a molten carbonate fuel cell, the mass-production and larger size of the electrolyte plate are demanded strong. However, in the aforementioned doctor blade method, since it takes a long time to evaporate the solvent, when large green sheets are being manufactured in large quantities, many doctor blade devices and long manufacturing time are necessary. Further, in the doctor blade method in which surfaces of the particles are covered by a binder in a slurry state to combine particles themselves, in order to form a sheet which is not cracked even after evaporation of the solvent, the binder is required to sufficiently fill the gaps between particles, that is, the addition of a large amount of the binder is required. Therefore, the cost goes up, and since a huge amount of hazardous gas is generated during degreasing of the huge amount of the binder, this is not recommended from an environmental point of view.
Thus, the doctor blade method, being slow in the manufacturing speed, is inadequate for making the size of the electrolyte plate larger and for mass-production thereof, moreover, since a huge amount of the binder is required, there are problems from the cost and environmental points of view.